The invention relates to a continuously operable sugar centrifugal having a centrifugal drum with an upwardly opening cone shape surrounded by a sugar collecting housing. At the upper wide conical end of the drum there are arranged sugar baffle elements surrounding a sugar discharge flange forming the upper end of the drum. These sugar baffle elements are secured to a rotatable ring which is equipped with means for influencing or controlling the r.p.m. of the ring.
Sugar centrifugals of the continuously operating type as mentioned above have been developed in recent years to a high level of performance. The throughput capacities of these centrifugals are very large and they produce a sugar having a degree of purity which is equal to that produced by periodically operating batch type centrifugals.
It is well known that a continuously operating production process is always more advantageous than a periodically or batchwise operating process. It is also well known that a continuously operating centrifugal is substantially simpler in its structure than a batch type centrifugal. Accordingly, continuously operating centrifugals are also more economical with regard to their initial investment expense and with regard to their operating costs as compared to batch type centrifugals. Nevertheless, continuously operating centrifugals have not been able yet to replace the periodically batch type centrifugals in the sugar industry, especially where the production of quality sugar is involved. This is so because the sugar crystals are damaged in continuously operating centrifugals when these crystals impinge upon the wall of the centrifuge housing as the sugar crystals fly off the upper drum edge at high speeds.
It is not practical to naturally decelerate the sugar crystals by friction with the surrounding air because such frictional deceleration would require a flight path of substantial length for the sugar crystals. This means that the housing of the centrifuge would require a diameter of several meters. Experiments in which the air friction was increased by increasing the air pressure or by means of directed air streams have not been successful in the attempt of catching the sugar crystals in the centrifuge housing without any danger of damaging the sugar crystals.
Other experiments to decelerate or deflect the sugar crystals have also been without success. Thus, in the centrifugal according to Austrian Pat. No. 268,164 it was intended to provide a gentle deceleration and deflection of the sugar crystals by means of a rotatable ring which reaches with an inclined baffle surface into the flight path of the sugar crystals. Such gentle deceleration and deflection was supposed to even be improved by applying a deceleration to the ring and by exposing the sugar crystals to an air stream. However, the desired result could not be achieved because any sliding contact between the sugar crystals flying at high speed and the solid surfaces of the baffle ring resulted in an abrasion of the sugar crystal surfaces, thereby dulling the crystals. Additionally, a sugar crust was very rapidly formed on the solid surfaces due to the sugar abrasion so that centrifugals as disclosed in Austrian Pat. No. 268,164 became inoperable even after short operating periods.
The same result has been noticed in connection with a centrifugal disclosed in German Patent Publication (DE-AS) 2,026,479. The centrifuge according to this reference is equipped with a rotatable ring carring vane type curved deflection plates. These deflection plates are intended to initially extend parallel to the flight path of the sugar crystal and to then gradually merge into the flight path with an ever increasing curvature in order to cause a deflection or detouring of the sugar crystals. In such an arrangement the kinetic energy of the sugar crystals is transmitted at least partially through the deflection plates to the rotatable ring. However, the sliding contacts between the surfaces of the solid deflection plates and the sugar crystals again produce a crystal abrasion with the resulting dulling and with a rapidly growing incrustation on these deflection plates.
In addition to the above described attempts of the prior art to solve the problems encountered in connection with the damage to the sugar crystals in continuously operating centrifugals, it has been suggested heretofore to construct the baffle elements of flexible or elastical materials such as synthetic materials or rubber. Reference is made in this connection to German Utility Model (DE-GM) 1,927,179. Such baffle elements of rubber or synthetic material however have not been capable of withstanding the very heavy mechanical wear and tear to which they are exposed. Thus, these elements were very rapidly destroyed in the operation of these centrifugals. In the sugar centrifugal according to said German Utility Model a baffle ring is located adjacent to the output end of the centrifugal drum. The baffle ring is made of a soft material or its surface is covered by a soft material. In any event, the soft material is rapidly destroyed.
Experiences gathered in years past in connection with continuously operating solution centrifugals support the conclusion that baffle elements made of synthetic material or rubber must be destroyed in very short periods of time. Such solution sugar centrifugals are equipped, instead with the above mentioned known baffle rings provided with a soft inner coating, with a curved baffle ring on which the sugar crystals are intentionally mechanically comminuted. It has been found during the testing time that these baffle rings which have been initially made of normal steels, exhibited even after a single campaign wear and tear zones having a depth of many millimeters. Stated differently, these baffle rings of normal steel were destroyed after a single campaign. Thus, it was necessary to use special steels for producing baffle rings capable of withstanding the mechanical wear and tear. Thus, it is understandable, that the baffle elements made of rubber or synthetic material do not stand a chance to withstand the wear and tear imposed on these rings by the sugar crystals.